seccomp: support 32-bit arm on arm64, and 32-bit ppc on ppc64

seccomp: support 32-bit arm on arm64, and 32-bit ppc on ppc64

Generally we enforce that a [arch] seccomp section can only be used on [arch].
However, on amd64 we allow [i386] sections for i386 containers, and there we
also take [all] sections and apply them for both 32- and 64-bit.

Do that also for ppc64 and arm64.  This allows seccomp-protected armhf
containers to run on arm64.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>